This object is achieved by providing, for each yarn entering the processing machine, at least an individual controlled tensioner and an individual tensiometer. At least the controlled tensioner and the tensiometer for a respective yarn are integrated into a closed yarn tension feedback regulation loop for regulating and maintaining a set yarn tension, and at least the tensiometer is connected in parallel to at least one superimposed common tension monitoring and setting system for centrally setting and monitoring the yarn tension in each yarn.
According to the invention the yarn tension in each yarn is individually measured and adjusted with a view to the yarn tension in the other yarns such that a very uniform yarn tension is assured for all the yarns simultaneously entering the processing machine. Each tensiometer also functions as a yarn breakage detector so that no additional yarn detectors are needed. The system automatically takes care of adjusting and maintaining the desired tension. Each individual controlled yarn tensioner in the closed regulation loop adjusts the yarn tension guided by the tensiometer such that finally the downstream tensiometer measures the correct yarn tension and can inform the superimposed common tension monitoring and setting system accordingly. The yarn tension for the plurality of yarns is kept exactly at the desired value or within a predetermined range. Alternatively, the yarn tension over time may be maintained within a predetermined relation to other yarns belonging to a yarn group of essentially equal yarns. The system may allow that a detected difference between the highest and lowest yarn tensions among the yarns in the yarn group does not exceed a certain percentage. The closed feedback regulation looping co-action with the tension monitoring and setting system allows maintaining the desired very precise yarn tension over time. The individual conveyors of the plurality of yarns, expediently, are operating synchronously. In the closed yarn tension feedback regulation loop of each yarn the set absolute or average value of the yarn tension is the guiding parameter of the regulation carried out by the co-operation between the tensiometer and the controlled tensioner. The regulation loop is closed by the yarn itself. Any occurring out of value or out of range condition is registered by the common tension monitoring and setting system and can be used to immediately stop the yarn processing system or initiate another action.
Expediently, each regulation loop or a regulator in the respective closed regulation loop is connected to an input of an interface assembly, which either is connected to or is integrated into the tension monitoring and setting system. The communication between the interface assembly and the closed regulation loops is bi-directional as is the communication between the interface assembly and the tension monitoring and setting system. The regulator of each closed regulation loop e.g. could be integrated into the interface assembly, or the interface assembly could be integrated into the tension monitoring and setting system.
Preferably, the interface assembly has a series of discrete input ports serving as connection terminals for the closed regulation loops, while a single output/input port could be used for the communication between the interface assembly and the tension monitoring and setting system.
In an expedient embodiment a regulator is contained in each closed regulation loop. The regulator may include at least one signal evaluation circuitry. Instead of placing the regulator in the regulation loop, the regulator could be placed in the interface assembly. The evaluation circuitry serves to evaluate the measured value of the yarn tension output by the tensiometer and to control the activation intensity of the controlled yarn tensioner accordingly. The regulator then adjusts the activation intensity for the controlled yarn tensioner depending on the actually measured value of the yarn tension. The conveyor placed upstream of the controlled yarn tensioner already may even out yarn tension fluctuations at the upstream side, e.g. resulting from a varying yarn bobbin diameter, spooling irregularities of the yarn on the storage bobbin, etc. This means that the conveyor already presents the yarn for the further processing by the yarn tensioner with a relatively uniform basic yarn tension facilitating the work for the controlled yarn tensioner to adjust precisely the needed yarn tension by guidance from the tensiometer.
In a preferred embodiment the conveyor is a positive or non-positive yarn feeding device. Such yarn feeding devices (normally implemented in weaving or knitting appliances) fulfill a very important yarn tension smoothing task in a yarn processing system, which simultaneously processes a plurality of running yarns.
In an expedient embodiment, the yarn feeding devices implemented as the individual conveyors are yarn feeding devices, which are normally used in rapier or projectile weaving machines. The stationary storage drum of the yarn feeding device carries several yarn windings consecutively formed by the winding element and present the yarn for further withdrawal with a relatively constant and predetermined basic yarn tension when it is withdrawn via the controlled tensioner into the processing machine. The driven winding element in co-action with the electronic speed control does not only even out yarn tension variations at the upstream side of the yarn path but also prepare a just sufficiently large yarn store on the stationary storage drum to cope with the consumption in the processing machine.
The electronic speed control of the yarn feeding device may be connected to the closed regulation loop, e.g. for an advantageous co-operation with the downstream controlled yarn tensioner and the tensiometer and as well with the interface assembly and/or the tensioning monitoring and setting system.
In another (not shown) alternative embodiment, the individual conveyors are excluded from the yarn processing system, which could be achievable in applications where a sufficient continuous input yarn tension to the respective controlled tensioner and tensiometer combination is maintained by drawing or feeding the yarn directly from the yarn stores, e.g. the yarn bobbins.
Expediently, the controlled tensioner is an electronically controlled yarn tensioner, e.g. actuated by a step motor or a permanent magnet motor. A deflection tensioner varies the deflection of the yarn while it runs through. A clamping tensioner varies the clamping force imparted on the yarn while the yarn is running through a tensioning zone of the clamping tensioner. Expediently, the clamping tensioner may be a TEC-tensioner available from the applicant. An electronically controlled yarn tensioner assures short response time, precise variations of the tensioning effect, low power consumption and high reliability.
Expediently, the controlled yarn tensioner is mounted to the exit side of the yarn feeding device. This avoids additional deflection points in the yarn path and allows controlling the yarn tension where the yarn is leaving the yarn feeding device.
Expediently, the tensiometer is provided downstream of the controlled tensioner, because it has to survey and control the yarn tension as adjusted by the controlled yarn tensioner. Preferably, the tensiometer even may be integrated into the controlled tensioner, such that additional deflection points in the yarn path as needed for the action of the tensiometer are avoided.
Expediently, the tension monitoring and setting system is integrated into the processing machine. A perfect location for the tension monitoring and setting system would be the machine control system. This allows the use of the normally provided indicating and setting section, screens, etc. of the machine control system for the additional task of the tension monitoring and setting system.
Alternatively, the tension monitoring and setting system could be arranged separate from the processing machine. This tension monitoring and setting system then may be constituted exactly for this task only. In this case it might also be expedient to have a communication connection between the separate tension monitoring and setting system and the machine control system.
In an expedient embodiment the tension monitoring and setting system is combined with an expert system. The expert system (e.g. known from patent application WO 2005/040470 A1) may have a collection of previously determined yarn tension settings associated to different yarn qualities and/or different yarn processing machines, e.g. in a table or list. Those previously determined yarn settings then will be available for the tension monitoring and setting system in the initial yarn processing system to more easily set optimum yarn tension values or yarn tension value ranges for all yarns or for yarn groups.
Expediently, the tension monitoring and setting system, particularly in the case that it is separated from the machine control system, may comprise a yarn tension setting/indicating section. This section may not only be used for executing settings of the respective yarn tensions, but also to show or display the actually measured yarn tension over time or the relation between yarn tensions of yarns within a yarn group, and the like. This computerised system also may be used to carry out recordings, e.g. to develop and store trends which result in failure conditions for later facilitating troubleshooting and the like.
At least one monitor should be provided at least for displaying for each yarn or for several at least substantially equal yarns of a yarn group the tension values, the tension value ranges, average tension values or tension profiles over time. The monitor greatly enhances the versatility of the system for operators.
In the tension monitoring and setting system the respective absolute value or a range for the absolute value or an average value of the yarn tension for each yarn or for a yarn group may be set. Of course, settings can be changed through the operation of the yarn processing system, e.g. in the case that the failure quota shows a tendency to increase.
Moreover, the settings may be carried out such that specific boundaries are fixed in the relationship between the yarns which belong to the same yarn group, such that the system during operation will allow fluctuations in the yarn tension between the yarns of the yarn group, but only to a certain extent as defined by limits representing severe failure conditions needing counter actions or a stoppage of the system. A counter action could be issuance of alarm signals. Another possibility would be to slow down the processing speed of the yarn processing system for a while, or to even switch off the system immediately. The program of the system could be intelligent enough to display advice or recommendations for corrections of the settings, e.g. during a waiting phase with reduced yarn processing system operation speed or after a shutdown of the yarn processing system. For this purpose, the tension monitoring and setting system may be connected to an alarm system, a processing system main switch, or a system operation correction assembly, accordingly, either directly or via the machine control system. In the latter case, the tension monitoring and setting system itself may initiate and execute operation correction measures.
Since it is expedient to use fast bi-directional communications among the components of the system or at least among several components of the system it is expedient to use at least one CAN-bus communication line. The CAN system allows achieving sufficiently high communication speed and data transmission rates with high system security and great reliability.
Since, in particular in case of a large number of simultaneously processed yarns, the tensiometers should be reliable but available for fair cost, according to an important embodiment the tensiometer is provided with a flexible element which is fixed at one end and is loaded at the other end by the yarn. The flexible element is a flexible printed circuit, which carries at least one sensor element, e.g. piezo-element or the like, which generates and transmits a signal corresponding or proportional to the load imparted by the yarn (the yarn tension). Finally, the flexible printed circuit should, at least partly, be coated with highly flexible temperature insulating and wear resistant material. This could be a polyimide film like KAPTON, poly(4,4′-oxydiphenylene-pyromellitimide). This type of coating essentially decreases the temperature influence to the sensor system, a factor that is very well known to the person skilled in the art. The flexibility of the coating is needed to not interfere with the load sensing property of the tensiometer by flexing the flexible element.